But should President Enrique Peña Nieto decide to strike back through other means, there are a number of avenues he could pursue.

US cooperation with Mexico on security matters has played an important role in Mexico's efforts to fight crime. Plan Merida, enacted in 2008, has provided the Mexican government $2.5 billion in funding, as well as training and equipment like Black Hawk helicopters. (Those resources are thought to have facilitated abuses as well.)

Mexico, however, has played an essential role in a number of initiatives vital to US interests. This includes not only drug interdiction and pursuit of organized-crime suspects, but intercepting and deporting the significant number of migrants from Central America who cross Mexico heading for the US.

Mexico is unlikely to halt its own fight against drugs and crime, but it could reduce or halt cooperation with the US on these programs.

"They could throw open the ports entry southbound and just let guns and cash flow in without inspection. They could make no effort to control the southern border. They could make a secret pact with drug-trafficking organizations. They could provide false intelligence, or no intelligence to the United States, in contrast to what they have been doing before," said David Shirk, a professor at the University of San Diego who researches crime and violence in Mexico.

"They could do any number of things to undermine the security of the United States. I don't think Mexico is likely to do those things because of the obvious negative ramifications," Shirk said, but there are "certainly many ways in which losing Mexico as an ally on security would be bad for the United States."

What, if any, official adjustment the Mexican government makes regarding security cooperation remains to be seen, but discussions about such changes are not just idle speculation.

"The drugs that come through Mexico from South America, or the drugs that are produced here in Mexico, all go to the United States. This is not our problem," Jorge Castañeda, who served as Mexico's foreign minister from 2000 to 2003, told CNN at the end of January.

US Secretary of State Colin Powell hugs Mexican Foreign Minister Jorge Castañeda, right, at the end of a joint press conference, November 26, 2002. REUTERS/Andrew Winning

"We have been cooperating with the United States for many years on these issues because they've asked us to, and because we have a friendly, trustful relationship."

"If that relationship disappears," Castañeda said, "the reasons for cooperation also disappear."

Much of the cooperation on security matters hinges on personal, on-the-ground relationships between Mexican agents and officials and their US counterparts.

These Mexicans may not give the orders, but they don't live and work in a vacuum.

"There's a great deal of individuals in both the military and the federal police, but I would say probably more so with the military, that are extraordinarily angered by everything going on with the Trump presidency," Mike Vigil, former chief of international operations for the US Drug Enforcement Administration, told Business Insider.

"And they have started to express disdain in terms of having to work with the US government based on that," Vigil said, adding:

"There's a lot people that've been expressing a reluctance moving forward, and that reluctance is becoming stronger and stronger as Trump continues to make remarks and continue with the deportation of not necessarily criminals, they don't have a problem with criminals, they understand that, but when they're separating Hispanic or Mexican families, women, mothers, fathers, who have absolutely nothing to do with any criminal activities. That is the arrow that pierces the heart of Mexican security forces."

Vigil stressed that friendships between Mexican and US officials may keep cooperation alive, but slights and insults from Trump may accumulate in the minds of Mexican security personnel until some have little motivation to act on tips or intelligence offered by the US. As Vigil explained:

"If you provide tactical information — let's say John Doe, or Juan Doe, is up here in, let's say, San Miguel de Allende, and we know what house he's in, we know he's definitely there — you pass it on to the Mexicans."

"They may not tell you 'no,' but they'll just drag their feet, and they'll let a lot of time pass by where the individual may have already moved, and that way ... you don't have a grievance. They're going to say, 'The guy wasn't there.'"

Immigrants from Central America answer questions from a US border patrol agent after crossing the Rio Grande from Mexico into the US on July 24, 2014, near Mission, Texas. John Moore/Getty Images

Amid Trump's looming crackdown on illegal immigration — no matter its origin— Mexican officials have identified the movement of people as an issue on which to counter the US's hardline toward Mexico, specifically on trade.

John Morton, director of the US Immigration and Customs Enforcement, stands near the entrance to a cross-border tunnel found in Otay Mesa, California, November 3, 2010. REUTERS/Nelvin C. Cepeda/San Diego Union-Tribune/Pool

"We have been a great ally to fight problems with migration, narcotics," Mexican Economy Minister Ildefonso Guajardo told The Globe and Mail in an interview earlier this month.

"If at some point in time things become so badly managed in the relationship, the incentives for the Mexican people to keep on cooperating in things that are at the heart of [U.S.] national-security issues will be diminished."

"You cannot ask me to [accept poor] conditions in terms of trade and then request my help to manage migration issues from other nations or … the prosecution of criminal activities and narcotics," Guajardo said.

"Mexico should stop doing the United States' dirty work on our southern border and stopping Central American minors or refugees or people fleeing the violence in Central America from going to the United States," Casteñada, the former foreign minister, told CNN this week.

"If they want to go to the United States, let them go," he said. "We should just let them through."

Though his time in office has been short, Trump's posture toward Mexico has inflamed much of the country.

Demonstrators hold a banner during a march to protest against US President Donald Trump's proposed border wall, and to call for unity, in Mexico City, Mexico, February 12, 2017. REUTERS/Jose Luis Gonzalez

In a poll of Mexicans conducted in late January by Mexican newspaper El Economista, 81.2% of respondents said they had a "bad" opinion of Trump — just one in 25 Mexicans said they had a "good" opinion of the US president.

The personal, business, and political ties between the two countries are many, and some people in Mexico are quite worried about the strain on the relationship, but Mexicans — among whom a sense of nationalism endures — may not accept the status quo indefinitely.

"I think that Mexico has been a good-faith partner to the United States up until the present, and Mexico needs the United States, and the United States needs Mexico," Shirk, who directs the Justice in Mexico program at USD, told Business Insider.

"But Mexico is a proud country, and at a certain point we will lose their good faith," Shirk said. "Mexico has to, at some point, I think, look out for itself."